Dr. Blair on Dyno Hill- Place your bets!

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My Duc S4 Monster 916 FI unfaired 101 HP factory advert says 147mph..

I have an old sports car that the speedo shows 180 MPH...;) When people ask "how fast will it go?" I always answer, "I've had it to an indicated 145 but the speedo says 180." They always ignore the 145 and comment, "180? Wow!"
 
acotrel said:
I have always been of the opinion that a good 500cc Manx is capable of doing about 130 MPH on a big race circuit. A fairing adds a few MPH.
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I don’t see what’s got folk in a tiz here Al?

Many sources quote the top speed of a period Manx at 130mph.

Classic Bike magazine road tested a new Molnar Manx some years ago, in that article Andy Molnar said one of his bikes would do 150mph on IOM gearing, the bike as tested was geared for short circuits and would do 125mph.

I can’t find any info on current IOM top speeds for a Manx. But modern 1000cc bikes are capable of 200mph and lap the IOM at 135+mph. So, if a Manx can lap at an average of 108+mph, a top speed potential in excess of 130mph seems quite likely to me.

Its hardly relevant to try and compare a tiny, minimalist, super slippery full faired race bike with a 100lbs jockey to a great big lardy road bike.

Years ago I learnt that folding the mirrors in on a GSXR 750 showed an indicated increase of nearly 5mph. A race bike has no such impediments to worry about.
 
2008 manx practice
Sulby Straight speed trap
s.lindsell paton 144.3
a reynolds " 134.2
a oversby norton 133.7
a brew seeley G50 131.1
p.coward weslake 130.8
c.swallow ducati 127.8
c.mcgahan G50 127.6
d.madsen-mygdal Ho 127.1
r.richardson 350 hon 125.7
m.parret G50 125.7
c.petty G50 125.4
B.PRICE G50 125.2
m.herbertson G50 125.0
 
Thanks Kommando.

So, nearly 134mph.

That was in 2008, so has presumably been bettered since. And I notice it was in practice.

I don’t know how being measured at the Sulby speed trap equates to potential maximum speed though. Anyone know ?
 
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I did the Classic TT last year for the first time on a Honda k4 350. My fastest speed down Sulby straight was just under 114mph - that's good apparently. The speed there is all about how much balls you have thro quarry bends. Hefyn Owen a younger racer and friend clocked 125mph the year before on his k4, the fastest in the 350 class. So 500 manxes will be doing 130mph for sure.
 
Of course we have to consider that what a Manx can do today is probably well beyond what an original Manx could do. So, IMO, the only valid test would be the Sulby straight with an original Manx (or one restored to exactly original spec - to include machining capability at the time).

An example of this in cars that I am thoroughly familiar with is a 1968 Hemi Barracuda - a limited production car that, off the 'showroom floor' in 1968, could turn 10.80s in the 1/4 mile with the 426 Hemi motor spinning to 7000 RPM and producing around 550HP. NOW, the same cars/engines turn in the 8.20's at 9000+ RPM producing over 1100 HP. This is all due to modern metals/materials/more precise machining. I suspect the same is true of a "current" Manx. What they get now out of the Manx's 500cc motor is probably considerably more than what they got out of it then.
 
Found a list somebody compiled from Cycle World road tests back in the day.

May, 1963, Triumph Bonneville TT special, 52 HP, 123.5 mph.
November, 1962, Manx Norton, 50 HP, 142 mph, a bit short of 150, but a lot more than 110.
October, 1962, Harley XLCH, 55 HP, 122 mph (only a street bike!)
August, 1963, Harley KRTT, 48 hp, 142 mph
August, 1963, Harley/Aermacchi 250 Sprint road racer, 28.5 hp, 116 mph
May, 1962, Honda CB77 Super Hawk, 28 hp, 105 mph. (another road bike!)
 
MexicoMike said:
Of course we have to consider that what a Manx can do today is probably well beyond what an original Manx could do. So, IMO, the only valid test would be the Sulby straight with an original Manx (or one restored to exactly original spec - to include machining capability at the time).

An example of this in cars that I am thoroughly familiar with is a 1968 Hemi Barracuda - a limited production car that, off the 'showroom floor' in 1968, could turn 10.80s in the 1/4 mile with the 426 Hemi motor spinning to 7000 RPM and producing around 550HP. NOW, the same cars/engines turn in the 8.20's at 9000+ RPM producing over 1100 HP. This is all due to modern metals/materials/more precise machining. I suspect the same is true of a "current" Manx. What they get now out of the Manx's 500cc motor is probably considerably more than what they got out of it then.
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Often wondered if a replica of Gresley's 1930's A4 steam engine was built with today's knowledge, materials and technology if there would be a significant increase in output.... and a new world record maybe?
 
Fast Eddie said:
I don’t know how being measured at the Sulby speed trap equates to potential maximum speed though. Anyone know ?
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Its the longest straight on a relatively flat incline, not sure if they can go faster coming down off the mountain as the straights are shorter but it does not count as its gravity assisted.
 
I think a carbureted bike jetted for maximum power at Sulby would be a bit rich and therefore a bit soft for the climb up the mountain, and as the mountain climb is a lot further than the Sulby straight it would be folly to jet for top speed along the straight.

Stinkwheels would need to be closer to good jetting for the straight otherwise they would seize but a 4 stroke could probably jet for the climb and suffer a small power loss for Sulby and therefor have a lower than max top speed.
 
I think the fastest bit is at the dip at the Highlander. Agree Storm but you can't really stop for a plug chop anywhere!
 
FastFred said:
I think the fastest bit is at the dip at the Highlander. Agree Storm but you can't really stop for a plug chop anywhere!
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We used Jurby airfield and got the jetting right there and then went down 1 size, the bike (GSXR750) went OK in the race.

Very hit and miss though.
 
storm42 said:
Found a list somebody compiled from Cycle World road tests back in the day.

May, 1963, Triumph Bonneville TT special, 52 HP, 123.5 mph.
November, 1962, Manx Norton, 50 HP, 142 mph, a bit short of 150, but a lot more than 110.
October, 1962, Harley XLCH, 55 HP, 122 mph (only a street bike!)
August, 1963, Harley KRTT, 48 hp, 142 mph
August, 1963, Harley/Aermacchi 250 Sprint road racer, 28.5 hp, 116 mph
May, 1962, Honda CB77 Super Hawk, 28 hp, 105 mph. (another road bike!)
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Of all those listed, I think the most terrifying ride would be the............................................XLCH.....
 
kommando said:
2008 manx practice
Sulby Straight speed trap
s.lindsell paton 144.3
a reynolds " 134.2
a oversby norton 133.7
a brew seeley G50 131.1
p.coward weslake 130.8
c.swallow ducati 127.8
c.mcgahan G50 127.6
d.madsen-mygdal Ho 127.1
r.richardson 350 hon 125.7
m.parret G50 125.7
c.petty G50 125.4
B.PRICE G50 125.2
m.herbertson G50 125.0
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The Paton might have a higher top speed, but I'd rather be riding the Manx. The Manx would probably lap faster. A Seeley G50 would be good, but different race class ? Have you seen the Steve Roper video with him and his mate both on G50s ? I think Steve was on the Matchless framed bike and his mate was on a Seeley with the same G50 motor. The Seeley was better going into corners. I think it had a disc on the front.
I think my Seeley 850 might be faster than a Manx on the IOM, but I would not like to be doing that with it. I'd be waiting for the crankshaft to kill me.
 
worntorn said:
How would those bikes do on Dyno Hill?
Can panniers be fitted for touring?

Glen
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So long as you’re in the right gear / right revs they’d fly up.

Drop out of the power band and they’d probably roll backwards !
 
I think the IOM sorts the men out from the boys. I don't want to be one of those men. When I was 23, I made a conscious choice between having a career as a professional scientist in Australia or going road racing in Europe with one of my mates. If I had gone there, I would probably have come home in an urn - NO BRAINS ! I still like going into corners too fast and getting on the gas too early. But I only ever do it on small race circuits, where top speed is irrelevant. Once you get over 100 MPH, you are asking for trouble - any crash is too big.
When I first started road racing, I rode at Phillip Island and had four major incidents in one day. I should have been stopped. I think of it mow and I am horrified at what I did. My friend had ridden the same bike at Bathurst in the 1950s and did a big number on himself. But I did not know the details of that until many years later.
 
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